RE: [TCML] Primary selfC

["Lau, Gary" <Gary.Lau@xxxxxx>]

Hi Bart,

Until Paul can speak to my earlier question, I think you're subscribing to the same false intuition that I and many, many others apparently do.

For a secondary coil (where we are more accustomed to discussing Cself), the value of Cself is not affected by the number or turns, the spacing of the turns, the diameter of the wire, or the dielectric between the turns.  All that matters is the geometry of the overall cylinder that contains the coil.  Try it with your favorite simulator!  No doubt the same is true for a primary coil as well.  This is why Paul was suggesting modeling the primary as a free-standing disk - the shape of the flat spiral primary.

I whole-heartedly agree - it sure does seem that the relationship between turns would be a dominant factor in Cself, but apparently it is not.

Regards, Gary Lau
MA, USA

> -----Original Message-----
> From: tesla-bounces@xxxxxxxxxx [mailto:tesla-bounces@xxxxxxxxxx] On
> Behalf Of bartb
> Sent: Thursday, July 24, 2008 9:59 PM
> To: Tesla Coil Mailing List
> Subject: Re: [TCML] Primary selfC
>
> Got to thinking,
>
> Didn't rolled caps have 2 metallic sheets rolled up? If so, then 1/2 the
> value, so 3.2nF and 940kHz. Chris, you can verify by measuring Fres and
> back calculating C from L.
>
> Bart
>
> bartb wrote:
> > Hi Paul, Chris,
> >
> > It might be more accurate to look at the total length of the ribbon
> > and width to determine area and treat it as rolled capacitor separated
> > by 1mm, using air as the dielectric, and determine C as one would with
> > any flat plate capacitor, but in this case, as a "rolled capacitor".
> >
> > C = 0.2248*k*A*(N-1)/(d*x)  (in pF)
> >    where
> >     k = Dielectric constant (1.0006 for air)
> >     A = Effective plate area in square inches (length x width)
> >     N = Number of conductive plates (3 for a rolled cap)
> >     d = individual dielectric film thickness (.03937" in this case)
> >     x = number of stacked sheets of dielectric between plates (1 in
> > this case)
> >
> > I think Chris is looking at about 6.4nF for the ribbon primary. So
> > he's probably correct to ask the question given the very low tank
> > capacitance. Primary C may be much higher than expected (a good deal
> > of area at about 557 square inches). Should be able to verify by
> > inserting a signal to the primary as one would with a secondary and
> > looking in the range of 470kHz assuming inductance is about 18uH.
> >
> > Regards,
> > Bart
> >
> > Paul Nicholson wrote:
> >> Chris Swinson wrote:
> >>
> >> > Does anyone know how to work out , or know of an online
> >> > calculator for crunching primary Self Capacitance ?
> >>
> >> Does JavaTC not give the Cdc of the primary?  If not,
> >> use JavaTC or FANTC to work out the self capacitance of a
> >> disk.
> >>
> >> Then, divide the Cdc by two to get an approximate effective
> >> capacitance.
> >> --
> >> Paul Nicholson
> >> --
> >>
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